i) Field of the Invention
The present invention relates to capacitors such as electric double layer capacitors and electrolytic capacitors each of which is provided with a pressure valve for emitting gas in an outer packaging case, and to methods for manufacturing the same.
ii) Description of the Related Art
A pressure valve for emitting gas in an outer packaging case is provided for a capacitor such as an electric double layer capacitor and an electrolytic capacitor. This pressure valve has a gas emission function and an explosion-proof function. A thin film is provided for a pressure valve in order to fulfill these functions. Generated gas in a capacitor is gradually emitted through this thin film. This is the gas emission function. In contrast, gas that is suddenly generated by anomalies in a capacitor extraordinarily increases the internal pressure in the case because the generated gas is beyond the gas emission function. In this case, the pressure of the gas bursts the thin film of the pressure valve; that is, opening of the pressure valve allows the gas to be instantly emitted into the outside. Thereby, the explosion-proof function is fulfilled.
Concerning a capacitor including such a pressure valve, Japanese Unexamined Utility Model Application Publication No. H03-110827 describes that a safety valve is attached to a cover of a case that houses a capacitor element, this safety valve is provided with an overhanging in the thickness of the cover, and the tip of this overhanging is matched with the surface of the cover.